Respiratory therapists may rely on various items of equipment to apply respiratory therapy to a patient. One particular respiratory therapy device delivers a medicated aerosol to a patient or applies a composite therapy involving alternation between continuous high frequency oscillation (CHFO) therapy and continuous positive expiratory pressure (CPEP) therapy each in conjunction with aerosol delivery. All three modes of operation (aerosol, CHFO, CPEP) involve some risk of cross contamination, i.e. contamination of the patient by a gas stream delivered by the therapy device, or contamination of nondisposable components of the device by the patient. Accordingly, it is desirable to develop ways to reduce the risk of cross contamination.